Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B28—WORKING CEMENT, CLAY, OR STONE
  • B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
  • B28B3/00—Producing shaped articles from the material by using presses; Presses specially adapted therefor
  • B28B3/20—Producing shaped articles from the material by using presses; Presses specially adapted therefor wherein the material is extruded
  • B28B3/26—Extrusion dies
  • B28B3/269—For multi-channeled structures, e.g. honeycomb structures
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/03—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the shape of the extruded material at extrusion
  • B29C48/09—Articles with cross-sections having partially or fully enclosed cavities, e.g. pipes or channels
  • B29C48/11—Articles with cross-sections having partially or fully enclosed cavities, e.g. pipes or channels comprising two or more partially or fully enclosed cavities, e.g. honeycomb-shaped
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
  • B29L2031/00—Other particular articles
  • B29L2031/60—Multitubular or multicompartmented articles, e.g. honeycomb

Definitions

• the present invention relates to extrusion dies for the continuous extrusion of fine honeycomb structures from plasticized inorganic powder mixtures, and more particularly to honeycomb extrusion dies comprising improved discharge slot surface finish profiles that impart more uniform and stable extrusion characteristics to the dies.
• inorganic honeycomb structures from plasticized powder batches comprising mineral or other inorganic powders dispersed in appropriate binders is well known.
• U.S. Patents Nos. 3,790,654, 3,885,977, and 3,905,743 describe dies, processes and compositions for such manufacture, while U.S. Patents No. 4,992,233 and 5,011,529 describe honeycombs of similar cellular structure extruded from batches incorporating metal powders.
• extrusion dies for the production of ceramic honeycombs by these methods requires extremely precise machining.
• the inlet or supply face of the die is provided with multiple apertures or feed holes into which the plasticized batch material to be extruded is forced under high pressure.
• the opposing discharge or outlet face of the die is provided with a criss-crossing array of finely machined discharge slots, these slots being cut into the discharge section of the die so that they intersect the holes of the feed hole array. These slots operate to finally shape the plasticized batch supplied through the feed holes into the interconnecting wall structure of the extruded honeycomb.
• pins The islands of material between the intersecting discharge slots that together form the outlet face of the die are sometimes referred to as "pins", since due to the removal of the slot material they appear as free-standing metal posts extending outwardly from the die interior.
• the discharge slots may be formed by sawing.
• the die is to be cut from a harder, slower wearing material such as stainless steel, electrical discharge machining or abrasive wheel slitting are more widely used.
• the discharge slots are formed through an electrical discharge maintained between a long, thin, traveling electrode wire and the metal die preform.
• EDM electrical discharge machining
• U.S. Patents Nos. 2,526,423, 4,205,213, 4,233,486, 4,403,131 and 4,527,035 provide detailed descriptions of EDM processing.
• Slot lengths formed by wire EDM in these dies can be 3-1/2 inches in length or more, and slot depths greater than 0.1 inches with slot widths of 0.012 inches or less can be provided.
• slots formed in stainless steels by EDM methods are substantially free of burrs and have a relatively smooth and consistent surface finish.
• the abrasive wheel slitting process typically involves the use of a diamond or other abrasive-impregnated cutting wheel to slice the narrow discharge slots into the face of the die.
• Abrasive wheel slitting produces discharge slots of substantially smoother surface finish than even EDM slotting, and has the further advantage that it is not subject to process disruptions from variations in electrical discharge conditions. Slots produced by this process should theoretically reduce slot flow rate variability to insignificant levels.
• U.S. Patent No. 5,320,721 discloses an electrochemical polishing process by means of which feed holes are smoothed to reduce batch flow resistance.
• WO 99/20445 teaches the use of a geometric feature impressed on the side surfaces of the discharge slots to reduce the incidence of honeycomb product defects.
• the present invention provides honeycomb extrusion die designs offering significant improvements in flow uniformity and stability, not only for the extrusion of very thin-walled honeycombs but for the extrusion of conventional honeycombs as well. These improvements result from the use of an improved discharge slot design incorporating "multi-textured" slot surfaces, i.e., slot surfaces formed by pins that incorporate surface regions of at least two different surface finishes.
• Multi-textured pin or slot surfaces are unexpectedly effective in suppressing batch flow irregularities arising from small, unavoidable variations in feedhole and discharge slot geometry or finish produced by prior art machining procedures. Further, multi-textured slot surfaces are a more cost-effective way to achieve exact substrate geometry than are known techniques for reducing the variability of such geometries.
• the multi-textured pin surfaces used in accordance with the invention include smooth surface portions of very low surface roughness in combination with somewhat less smooth portions of higher surface roughness.
• the smooth and less smooth surface portions are disposed serially along the length of the pin surfaces connecting the feedhole ends to the outlet face ends of the pins, so that plasticized batch material traversing the discharge slots from the feedhole inlets to the die outlet face traverses the surface portions of differing surface finish in sequence, one after the other.
• the invention includes a honeycomb extrusion die of modified slot design, which may be otherwise conventional with respect to its composition, overall geometry, and feed-hole design.
• the honeycomb extrusion die (10a) comprises a die body incorporating an inlet face, a discharge face opposite the inlet face, a plurality of feedholes (13) extending from the inlet face into the die body, and an intersecting array of discharge slots (17) extending into the body from the discharge face to connect with the feed holes (13), the intersecting array of discharge slots (17) being formed by the side surfaces of a plurality of pins (19a) bounded by the slots (17) and extending into the die body from the discharge face, characterized in that a plurality of the pins (19a) include one or more multi-textured side surfaces, said side surfaces including at least two surface regions (20, 21) differing in surface finish from each other, wherein the two surface regions (20, 21) include a first surface region (20) having a surface roughness below 0.5 micrometers (20 microinches) RA and a second surface region (21) having a surface roughness above 0.75 micrometers (30 microinches) RA.
• the discharge slots separate the outlet face into a plurality of pins, bounded by the slots and extending from the feedholes to the outlet face of the die.
• the side surfaces of a plurality of the pins defining the discharge slots for the die include one or more multi-textured side surfaces, said side surfaces including at least two surface regions differing in surface finish from each other.
• each of the multi-textured side surfaces may additionally include a flow-modifying surface feature such as a groove or ledge separating the two regions of differing surface finish, to further mask any flow differentials arising from feedhole irregularities, batch inhomogeneities, or the like.
• the invention offers an improved extrusion process which employs the modified flow characteristics of the die of the invention to form extruded honeycombs with fewer shape defects attributable to flow variations imparted by the die.
• a plasticized batch material is formed into a honeycomb shape, the method comprising forcing the material into a feed hole array (13) in an inlet face of a honeycomb extrusion die (10a) and flowing the material into and through a die discharge section, comprising a criss-crossing array of discharge slots (17) formed by an array of pins (19a) terminating at an outlet face of the die to form the material into the honeycomb shape, characterized in that the flowing material is formed at least in part by multi-textured side surfaces provided on at least a plurality of the pins (19a) in the array, each multi-textured side surface having at least two surface regions (20, 21) differing in surface finish from each other, the surface regions (20, 21) including a first surface region (20) having a surface roughness below 0.5 micrometers (20 microinches) RA and a second surface region (21) having a surface roughness above 0.75 micrometers (30 microinches) RA.
• the batch material is formed at least in part by multi-textured side surfaces provided on all or a plurality of the pins in the array.
• Each of the multi-textured side surfaces has at least two surface regions differing in surface finish from each other. Flow alteration by these multi-textured side surfaces appears to substantially contribute to the significant reductions in extrudate flow front variations which are observed. These reductions in turn reduce product defects such as swollen or undulating web (channel wall) surfaces in the honeycomb products caused by flow variations through the dies.
• Fig. 1 is a schematic perspective view in partial cross-section of a section of a conventional honeycomb extrusion die of the kind employed in the art for the extrusion of ceramic honeycombs.
• extrusion die 10 comprises feed holes 13 extending upwardly from a die inlet face (not shown) through which extrudable batch material is conveyed to feed hole/slot intersections 15, and from there into discharge slots 17.
• Discharge slots 17 then convey the batch material upwardly to outlet face 18 of the extrusion die where it exits the die in the configuration of a honeycomb.
• discharge slots 17 are bounded or formed by the side surfaces of pins 19, the latter being formed as the discharge slots are formed. It is the side surfaces of pins 19 which form the walls of the slots and thus the walls of the honeycomb shapes as the batch material is extruded from the die.
• Fig. 2 of the drawing is a schematic perspective view in partial cross-section of a section of a honeycomb extrusion die provided in accordance with the invention.
• extrusion die 10a again comprises feed holes 13 extending upwardly from the die inlet face and intersecting with discharge slots 17 at the base of the discharge section of the die.
• pins 19a bounding discharge slots 17 incorporate side surfaces having surface regions 20 and 21 that are of substantially different surface texture.
• upper or outer side surface regions 20 adjacent the terminal ends of the pins have very high smoothness, whereas lower or inner side surface regions 21 are somewhat lower in smoothness.
• pin side surfaces including a first surface region having a surface roughness below about 0.5 micrometers (20 microinches) RA and a second surface region having a surface roughness above 0.75 micrometers (30 microinches) RA will normally be used.
• Relatively smooth first surfaces within the prescribed surface roughness range may readily be produced by methods such as the abrasive wheel slitting process, while second surface regions with surface roughness values above about 30 microinches can be provided by conventional wire EDM slotting techniques.
• Some improvement in extrusion performance can be obtained without treating all side surfaces of all of the pins in the die to develop the desired surface textures.
• first and second surface regions on the pins are not believed to be critical. However, positioning the first (smoother) side surface portions closer to the die outlet face than the second surface portions, and preferably extending the first surface portions outwardly to reach the outlet face of the die as shown in Fig. 2, may have an advantage where optimum smoothness in the extruded webs of the honeycombs is desired.
• Also useful as optional features in the die designs of the invention are the geometrically designed, macroscopic, flow modifying pin surface discontinuities disclosed in published PCT patent application WO99/20445. These discontinuities, which may be provided as recesses or protrusions (e.g., grooves or ridges) on all or a plurality of the pin side surfaces, may be helpful to further stabilize batch flow through the slots. In the case of a recess or groove oriented parallel with the outlet face of the die, such a feature can conveniently be machined into the pin side surfaces by wire EDM procedures at the same time that a roughened surface portion is provided by EDM machining of the lower portions of the same side surfaces.
• Fig. 3 of the drawing illustrates a particularly preferred slot design of this type, showing two adjacent pins 19a with sidewalls forming a slot 17 and tops terminating at the outlet face of an extrusion die.
• pin surface multi-texturing on extrusion die forming characteristics is best illustrated by comparing the honeycomb extrusion performance of two examples of essentially similar dies, one example incorporating uniformly smooth pin surfaces and the other incorporating multi-textured pin surfaces formed by a combination of abrasive wheel grinding and EDM wire wheel finishing.
• two stainless steel honeycomb extrusion dies configured to form square-celled honeycomb products having a fired cell density of about 350 cells/in2 of honeycomb frontal area are selected.
• the discharge slots on the outlet surfaces of the dies have a slot width of about 0.0055 inches and a slot depth of about 0.100 inches.
• one of the dies (conventional) has a smooth slot configuration, substantially similar to that schematically shown in Fig. 1 of the drawing, while the second die incorporates slots with both smooth and rough surface regions, similar to that shown in Fig. 2 of the drawing.
• All of the slots in the first or conventional die are formed by abrasive BorazonTM wheel slitting, providing a very smooth and uniform slot finish to the full depth of the slots and across the entire outlet surface of the die.
• the slots in the second die are formed by a combination of BorazonTM wheel slitting and EDM refinishing to produce adjacent smooth and rough surface portions on the side surfaces of the pins.
• That die is first provided with slots of the full 0.100 inch depth by BorazonTM wheel slitting. Then, the inner or bottom portions of each slot are refinished by EDM wire machining. This is accomplished by positioning an EDM wire of about 0.004 inches diameter in each precut slot at a depth of about 0.05 inches below the outlet face of the die, and then refinishing those portions of the slot surfaces extending below that depth. At the same time, a shallow groove about 0.002 inches in depth is cut into the side surfaces of each pin at the boundary of the smooth and roughened slot portions, as a supplemental flow control measure.
• each pin has side surfaces including an outermost smooth surface portion having a surface roughness of about 5 RA and a second inner surface portion of higher slot roughness (about 70 microinches RA) generated by the EDM wire refinishing.
• honeycomb bodies of 350 cells/in2 cell density are formed with each die from a conventional ceramic batch material containing clay, talc and alumina mixed with organic binders in a water vehicle.
• Forming honeycombs at wall thicknesses below about 0.006 inches with such conventional batches is generally difficult, as demonstrated by the fact that the yield of "acceptable" product from the first extrusion die produced as above described (i.e., product acceptable for drying and firing) is typically in range of only about 30% of the material extruded.
• the remainder of the extruded product exhibits a variety of cell and cell wall shape defects known to be associated with flow irregularities through the die.
• the second die which incorporates the multi-textured slot design provided as above described, exhibits markedly better extrusion performance than the first die.
• Extrusion trials to produce 350 cells/in2 honeycomb product produce yields of greater than 90% of extruded ware suitable for drying and firing, from the same extrusion batch providing only 30% yields when formed using the first die. This result is directly attributed to a substantial reduction in defect-producing "fast flow" behavior caused by the improved slot design of the second die.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Chemical & Material Sciences (AREA)
• Ceramic Engineering (AREA)
• Press-Shaping Or Shaping Using Conveyers (AREA)
• Extrusion Moulding Of Plastics Or The Like (AREA)
• Extrusion Of Metal (AREA)
• Fertilizing (AREA)
• Eye Examination Apparatus (AREA)
• Nozzles (AREA)

Applications Claiming Priority (3)

Publications (3)

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Family Applications (1)

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• 1999
  • 1999-09-23 US US09/401,713 patent/US6299813B1/en not_active Expired - Lifetime
• 2000
  • 2000-08-28 AU AU70831/00A patent/AU7083100A/en not_active Abandoned
  • 2000-08-28 EP EP00959521A patent/EP1226014B1/en not_active Expired - Lifetime
  • 2000-08-28 WO PCT/US2000/023608 patent/WO2001021379A1/en not_active Ceased
  • 2000-08-28 CN CNB008131805A patent/CN1189307C/zh not_active Expired - Lifetime
  • 2000-08-28 DE DE60017177T patent/DE60017177T2/de not_active Expired - Lifetime
  • 2000-08-28 AT AT00959521T patent/ATE285886T1/de not_active IP Right Cessation
  • 2000-08-28 JP JP2001524785A patent/JP5027972B2/ja not_active Expired - Lifetime
• 2002
  • 2002-02-14 ZA ZA200201261A patent/ZA200201261B/xx unknown

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